Head gasget thickness
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Elder User
Joined: Nov 2004
Posts: 726
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From: So. California
Head gasget thickness
I am doing my heads right now for my 359 (351 .050" over) and was wondering how thin of a head-gasget I can run. I have heard of steel shims that can be as thin as .010" thick. I just can not find any for the small block ford. My piston to deck clearances are .020", .018", .015", .018", .029", .024", .021" and .023". I am considering dismantling my short-block and having the deck milled. I am most likely going to have my heads milled for $75. and the block milling will cost $100. I am aiming for a tight quench distance of about .040". Is there any gain of going tighter? I do not want this motor to ping and I am looking at running a Schneider 262/262 hydraulic flat-tappet camshft
208/208
112 Lobe seperation angle.
208/208
112 Lobe seperation angle.
Cargo Master
Joined: Jun 2001
Posts: 2,571
Likes: 22
From: Oxford, Indiana
As you've already figured out, good quench is key to knock resistance. My preference is to ALWAYS get the deck milled for zero deck clearance and then run a Felpro 1011-2 head gasket. That gasket is a good quality piece and one of the thinnest I've found at .039" compressed thickness. That puts your quench right in the sweet spot. And yes, with your deck clearance numbers that whacked out, I'd definitely have the deck straightened out. I'd make that a priority over having the heads milled. By my calculations, your .014" difference from the highest to the lowest can result in about 3/10ths of a point difference in compression. That's quite a bit. If you do both, just remember that you don't want the combined total material removed to exceed about .025 or you will need to get the intake corrected also and have the bolt holes spotted.
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Elder User
Joined: Nov 2004
Posts: 726
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From: So. California
I have been decking my block with a large plate of glass with fine sand paper glued on it. I can say that it makes the deck look better. I called two shops and both required my block be bare prior to milling it. One shop where I had my valve-seats cut wanted $100. to mill both decks individually to whatever specification I wanted. The other shop wanted $140. to do the same thing. Why couldn't I have the assembled short block decked? Would .010", .020" be any better than .040"? The overwhelming majority of information I read says that .040" from the combined piston in the hole distance + head gasget compressed distance. How does a 13.2 cc dish factor into the quench and detonation science?
Cargo Master
Joined: Jun 2001
Posts: 2,571
Likes: 22
From: Oxford, Indiana
Running much less than .040" quench doesn't provide any additional benefit, but it does start making things tight. If you have it machined for zero deck clearance and then run a .010" shim gasket, you'll probably end up with piston-to-head contact. The rod and piston assembly expands and gets longer as it heats up. Add a little carbon buildup into the equation and it doesn't take long to close up .010". Unless your pistons have a full dish, it really won't effect quench. Even a dished piston normally has a flat area that corresponds to the flat quench area in the combustion chamber of the head.
